But use of the drug has raised concerns over rider safety, as side effects include drowsiness and loss of concentration which could cause crashes in the tightly-packed peloton.

Tramadol users also face gradual dependence on the substance with the risk of developing addiction.

The drug is not included on WADA’s list of prohibited substances, despite calls for it to be banned.

WADA says it is not convinced tramadol has performance-enhancing benefit, but that it could be banned in the coming years.

Instead tramadol is listed on the WADA Monitoring List, where it has remained since 2012.

According to a WADA study carried out in 2017, 4.4 per cent of in-competition tests on cyclists showed the used of tramadol, while 68 per cent of urine samples taken from 35 Olympic sports that contained the drug were taken from cyclists.

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